Attempts have already been made to use a flow-multiplier effect by projecting a flow of water directed towards a nozzle, an orifice, or a cone for the purpose of entraining water and thus obtaining a high flow rate for water circulation.
Thus, document U.S. Pat. No. 4,501,659 describes an appliance for circulating water in a swimming pool so as to enable the water to be filtered. As shown in accompanying FIG. 1, which reproduces a figure of that document, the top portion of the appliance comprises a filter and the bottom portion of the appliance is connected to a supply of water under pressure and includes a nozzle assembly directed towards an outlet opening in a facing wall. A converging portion or spout may be placed facing the ejector. It is located towards the bottom of the appliance. Water that has passed through the filter approaches the ejector from one side thereof and changes in direction in order to pass into the spout. The flow-multiplication factor that is obtained is relatively small, and it never exceeds 2.5.
Document U.S. Pat. No. 4,826,591 also describes a swimming pool filter installation, as shown in accompanying FIG. 2, which reproduces a figure of that document, in which installation a pump causes a flow of swimming pool water to circulate through a filter. Before returning to the swimming pool, the water passes through an ejector or restricted nozzle placed in front of a converging portion or entrainment nozzle so that the water which has come through a basket connected to a skimmer is sucked in by the converging portion. In that system, the flow obtained by multiplication is not used for circulation through a filter, but only through a basket for stopping debris such as leaves. As in the preceding document, the ejector and the converging portion are placed close to a bottom surface of a space whose top portion houses the basket. As indicated by arrows, the water moves down towards the inlet of a converging portion disposed horizontally, where it changes direction. Although the body of that document does not specify the multiplication ratio obtained with such a system, the values given for the various dimensions correspond to a multiplication factor that is small, certainly not exceeding 2.5.
Document U.S. Pat. No. 5,785,846 also describes an installation, as shown in accompanying FIG. 3, which reproduces a figure of that document, in which installation a pump feeds an ejector that projects a flow of water towards a duct facing it and in alignment therewith and disposed in a chamber that defines a rounded converging portion leading to the inlet of the duct. The suction effect created by the ejector in the converging portion is used for sucking in water that has passed through a filter and that arrives via a duct opening out into the side of the chamber surrounding the ejector. As shown in that figure, the flow of water coming from the filter arrives on one side of the ejector and is subjected to a change in direction through 90° in order to be entrained towards the outlet duct. Although the document gives no value for the flow-multiplication factor, the highly asymmetrical water inlet certainly puts a limit on the flow-multiplication factor at well below 2.5.
Document WO 02/086259 describes a flow-multiplier water circulation assembly, part of which is shown in accompanying FIG. 4 which reproduces one of the figures of that document, which assembly gives a multiplication factor greater than 2.5, and that can even exceed 3. That flow-multiplier assembly comprises a converging portion, a throat, and a diverging portion, and water under pressure is injected in a direction that is parallel to the inside surface of the throat through a slot disposed at the periphery of the throat. That system is limited to injecting water into the throat, and given the great length of the slot formed around the throat, the slot must be very narrow; in practice, it is found that it is easily clogged, unless appropriate precautions are taken to ensure that it does not become clogged.
Document WO 03/062561 which in the context of the present invention should be taken into consideration only under EPC Article 54(3) [prior filing date], describes an improvement to the system disclosed in the preceding document. As shown in accompanying FIG. 5, which reproduces one of the figures of document WO 03/062561, that system comprises an assembly having a converging portion, a throat, and a diverging portion including a first ejector disposed at the inlet to the converging portion, and a second ejector disposed in the throat. That system thus combines two injections, firstly via an ejector on the axis of the converging portion, the throat, and the diverging portion, and subsequently by the throat ejector. In addition, that document states that the upstream ejector placed on the axis of the converging portion may be located inside a Kaplan bend so as to enable a high flow-multiplication ratio to be obtained. As indicated in the figure, a flow at a rate of 10 cubic meters per hour (m3/h) inserted half into the upstream ejector and half into the throat ejector gives an outlet flow at a rate of 30 m3/h, i.e. that the flow-multiplication ratio is equal to 3.